Schistosomiasis, a debilitating parasitic disease caused by flatworms of the genus Schistosoma affects 200 million humans, with 600 million more at risk. No vaccine is available. Current control efforts emphasizing mass chemotherapy yield welcome relief of human suffering but can render the existing drugs ineffective by selecting for resistant schistosomes. Long term control of this global health problem will benefit from reduction of new schistosome infections. Schistosomiasis is transmitted by snail intermediate hosts such as Biomphalaria glabrata in which the parasites undergo obligatory development. A long term objective of this proposal is to characterize determinants for suitability of snails as host for schistosomes. Insight into the potential of local snail populations to support development of schistosomes allows monitoring, predicting and possibly limiting transmission of schistosomiasis, and could focus control efforts on areas with increased risk of schistosome transmission to optimize use of limited resources for (global) health management. I aim to fill in gaps in the understanding of the snail host-schistosome compatibility by continuing study of effector components and regulation of immune response capabilities of B. glabrata. Previous transcriptome analysis revealed many (new and putative) immune factors, indicating that B. glabrata has potent multi-faceted immune capabilities. However, relative to other pathogens, B. glabrata responded modestly to compatible schistosomes. This suggests that regulation of the response was incomplete or ineffective. Microarrays and custom macroarrays will be used to identify common factors of general effective immune responses in both schistosome resistant and susceptible B. glabrata strains. Special attention will be directed to putative immune factors among novel (unknown) sequences to expand understanding into immunity of B. glabrata. Up to 10 (groups of) candidate defense genes will be characterized by full-length cDNA sequencing; detailed study of expression over time in response to immune with (in)compatible schistosomes or bacteria; RNAi knockdown to investigate phenotypic changes regarding anti-pathogen responses, and in-situ hybridization to localize expression in B. glabrata (untreated, challenged and following RNAi knockdown). BAC clones containing upstream regions of established and novel immune genes will be analyzed for regulatory sequences, using gel shift assays with nuclear extract from immune-stimulated snails to confirm function. Transcription factors will be purified and analyzed using proteomics. Expression of transcription factors in response to immune challenge will be tested in schistosome susceptible and resistant snails. Finally transcription factors will be targeted by RNAi to investigate the contribution of affected genes to anti-schistosome responses in a resistant snail. Recent technical developments justify the proposed use of these highly sophisticated methods. Any data forthcoming from the ongoing B. glabrata genome sequencing will further facilitate this study of immune function of B. glabrata in the context of transmission of schistosomiasis.